Method for preserving image detail when adjusting the contrast of a digital image

Abstract

A method for preserving detail when adjusting tone scale of a digital image channel, the method comprises receiving a digital image channel; providing a tone scale function for adjusting the tone scale of the digital image channel; spatial filtering the digital image with a spatial filter which varies with location in the digital image channel according to the control signal producing a space-variant spatial filtered version of the digital image channel; using the tone scale function and the space-variant spatial filtered version of the digital image channel to produce an enhanced digital image channel.

What is claimed is:  
     
       1. A method for preserving detail when adjusting tone scale of a digital image channel, the method comprising: 
       (a) receiving a digital image channel;  
       (b) providing a tone scale function for adjusting a tone scale of the digital image channel;  
       (c) spatial filtering the digital image channel with a spatial filter which varies with location in the digital image channel according to the value of a control signal, thereby producing a space-variant spatial filtered version of the digital image channel; and  
       (d) using the tone scale function, and the space-variant spatial filtered version of the digital image channel to produce an enhanced digital image channel.  
     
     
       2. The method as in claim  1  further comprising creating the control signal from a spatially filtered version of the digital image channel. 
     
     
       3. The method as in claim  2 , wherein step (a) includes generating a high pass and low pass signal; wherein step (b) includes generating at least two non-linear spatial filtered versions of the digital image channel from the high pass signal, the low pass signal, the control signal, and the digital image channel. 
     
     
       4. The method as in claim  3 , wherein step (a) includes generating an enhanced digital image channel by application of the tone scale function to one of the non-linear spatial filtered versions of the digital image channel, and wherein step (b) includes adding the remaining non-linear spatial filtered versions. 
     
     
       5. The method as in claim  3 , wherein step (a) includes generating an enhanced digital image channel by application of the tone scale function to one of the non-linear spatial filtered signal versions of the digital image channel, and wherein step (b) includes modifying the remaining non-linear spatial filtered signals, and wherein step (c) includes adding the non-linear spatial filtered signals. 
     
     
       6. The method of claim  1 , wherein step (a) includes receiving a luminance channel as the digital image channel. 
     
     
       7. The method of claim  1 , wherein step (a) includes receiving either a red, green and blue channel as the digital image channel. 
     
     
       8. The method as in claim  7 , wherein each of the red, green and blue channels are received steps (b)-(d) are performed on each of the red, green and blue color channels.